My invention pertains to a protective electrical discharge device. More specifically, the invention relates to a lightning arrester for protecting low voltage circuits, e.g., railroad signaling circuits and/or apparatus, against voltage surges, particularly from lightning during electrical storms.
Railroad signaling circuits in particular are exposed to the hazards of electrical storms so that, to maintain proper and safe operation, they require adequate protection against voltage surges due to lightning and other external causes. Protective electrical discharge devices, e.g., lightning arrestors of various types and using various materials, for both line-to-line and line-to-ground protection, have long been used to protect such low voltage circuits and apparatus. The advantages of employing varistors, i.e., non-linear resistors, for protection of electronic circuits against surges and transients caused by lightning or electrical power switching and faults have also been recognized. These advantages include, but are not limited to, fast response time and the ability to slowly dissipate static charge buildup. A major problem in the use of varistors has been their relatively low energy/volume ratio, necessitating very large and expensive varistors in those applications where the varistor is exposed to very large energy surges. A method or arrangement whereby smaller, less expensive varistor elements can be used will thus provide operational and cost advantages.
Accordingly, an object of my invention is an improved protective electrical discharge device using a varistor element.
Another object of the invention is a lightning arrester incorporating a varistor element which is paralleled by an air gap.
A further object of my invention is an electrical surge protector device in which low voltage surges are dissipated or passed by a low energy varistor element which is supplemented for higher voltage surges by a parallel air gap which passes the large energy levels to protect the varistor element from damage.
Yet another object of the invention is a low voltage lightning arrester device in which a varistor element, press-fitted into recesses in opposing surfaces of metal electrodes to establish a predetermined air gap, passes static voltage buildup and low voltage surges until the surge voltage buildup causes the surge energy to be passed by the air gap, from metal-to-metal surface, so that the bulk of the surge current is shunted away from the varistor.
Other objects, features, and advantages of my invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawings.